1. Technical Field
The present invention relates to a robot system and a cable.
2. Related Art
In a robot system, a control unit and a robot are connected via a cable and the control unit controls the robot via the cable. As the cable, for example, a motor drive cable is used.
Regarding the motor drive cable, development has been conducted (see Patent Document 1 (JP-A-2005-267873) and Patent Document 2 (International Publication No. 2008/041708)).
The motor drive cable has a power line and a frame ground (FG line). A conductive noise current flows via capacitance parasitic between the power line and the FG. The current is specifically a common-mode switching noise current. A mechanism of generating conductive noise by switching for driving motor is described in, for example, Patent Document 1 (see Patent Document 1). Normally, parasitic capacitance increases in proportion to the length of the cable.
Patent Document 1 discloses that, when a motor is driven using a power converter, in a power cable of supplying power from a power source to the power converter or from the power converter to the motor, respectively insulated power lines of respective phases are bundled together and an insulator containing a core member of a magnetic material covers around the power lines (see Patent Document 1). However, the technology disclosed in Patent Document 1 is insufficient as measures for conductive common-mode noise in the motor drive cable that drives a plurality of motors.
Patent Document 2 discloses a motor drive cable with a high frequency leak current return wire in which the inductance of a high frequency leak current return wire is reduced by arranging an insulated core wire for driving consisting of a plurality of lines in close proximity to and adjacent to a high frequency leak current return wire consisting of one to a plurality of lines, and, at the same time, the insulated core wires for driving and the high frequency leak current return wires are arranged substantially in parallel in the length direction and stranded before a sheath is applied to the outside of the stranded wires with no intervention of a shield (see Patent Document 2). However, in the technology disclosed in Patent Document 2, focus is mainly placed on the inductance parasitic in the cable, and the technology addresses the noise (radioactive noise) with a higher frequency than that of the conductive noise and is insufficient for the conductive noise.